#include <iostream>
#include <string>
using namespace std;

int main() {
  string N; cin >> N;
  string ideal(N.size()-1, '3');
  if(N.size() == 1) {
    cout << -1 << endl;
  } else {
    if(N[0] == 1 && N.substr(1) == ideal) {
      cout << ideal.size() << endl;
    } else {
      cout << -1 << endl;
    }
  }
  return 0;
}